ProjectSummary:Theprimarygoalofthisproposalistodevelopandapplyaninvitromodelofthe neuromuscularjunction(NMJ)usingmotorneuronsandmusclebothderivedfromhumaninduced pluripotentstemcells(iPSCs).Theresearchwillcombinestate-of-the-artstemcellbiology,gene targeting,electrophysiologyandgenomictechniques.Themainfocusoftheapplicationwillbein amyotrophiclateralsclerosis(ALS),commonlyknownasLouGehrig?sdisease,whichisadevastating diseaseofthemotornervoussystemwithanonsetoftenintheprimeoflifeandanaveragesurvivalof onlytwotothreeyears.ALSaffectsabout20,000peopleintheUSatanytime.About10%ofcases areduetodominantfamilialmutationsand90%areapparentlysporadic.DegenerationoftheNMJis theearliestpathologicalfeatureofALSinbothhumansandmousemodels.Involuntarymuscle contractions,knownasfasciculations,arethefirstclinicaldiseasesymptomandreflectabnormalmotor neuronelectricaldischarges,whichoriginateinthedistalaxonandNMJ.TheNMJnovelmodelbrings tobeartheadvantagesofhumanstemcellapproaches,namely,toovercomelimitsofmousemodels includingartifactsthatresultfromheterologousover-expressionofhumanproteinsinamouse backgroundandinabilitytocapturecomplexitiesofdiversehumangeneticbackgroundsinmice. Furthermore,mousemodelsarelimitedtothefamilialformsofthedisease,whileiPSC-basedmodels havethepotentialtoaddresssporadicdisease,thevastmajorityofALScases.Theapplicationsofthe modeldescribedintheprotocolincludeidentifyingmorphologicalandgenomicphenotypesoftheALS NMJ,determininghowthemotorneuronandmuscleeachcontributetoabnormalmotorneuron physiologyandreciprocallyhowabnormalmotorneuronexcitabilityaffectstheNMJ.Thesequestions willbeaddressedacrossarangeoffamilialandsporadicALSvariants.Whilestillclearlyreductionist, themodelgoesbeyondisolatediPSC-derivedmotorneuronstoaddthedisease-relevantanatomical contextoftheNMJandthusgiveadditionalstructuralmeaningtoneuronalcomponentsliketheinitial axonsegment,axonanddistalmotorterminalsandmechanisticprocessesimplicatedinALSsuch axonaltransport.ThehumanNMJmodeldevelopedintheproposedprojectwillbeusefultoidentify specificALSsubgroupsthatsharecommondiseasemechanismsandtofindtargetsandevaluate candidatetherapeuticsappropriateforthoseindividualdiseasesubgroups.Themodelwillalsobe broadlyapplicabletoothermotorneurondiseases,suchasspinalmuscularatrophy,aswellasmotor neuropathiesandmyopathies.